JP3399755B2 - Polarizing beam splitter and liquid crystal projector including the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization beam splitter and a liquid crystal projector.

[0002]

2. Description of the Related Art Conventionally, as means for separating non-polarized light emitted from a light source into P-wave and S-wave having different polarization planes, for example, a multilayer thin film is vapor-deposited on the slopes of two prisms and an adhesive is applied to these. Cube-type polarization beam splitters are generally known. This multilayer thin film is formed by alternately depositing a film having a high refractive index and a film having a low refractive index. The refractive angle is determined by the selection of the refractive index, and the reflectance of the multilayer thin film is P-wave depending on the Brewster's condition. The polarization component of is close to 0%, and the polarization component of the S wave is close to 100%.

At this time, in the above-mentioned multilayer thin film, the refractive index of the film having a high refractive index is n _H , the refractive index of the film having a low refractive index is n _L , the refractive index of the prism is n ₀ , and the light is incident on the multilayer thin film surface. If the angle is θ ₀ , the condition for the reflectance of the P wave component to be 0 is

[0004]

[Equation 1]

[0005] At this time, when the incident angle θ ₀ is 45 °,

[0006]

[Equation 2]

The refractive indexes of the prism and the film may be selected so that For example, as a film having a high refractive index, ZnS
(N _H = 2.3), quartz stone (n _L =
If 1.35) is used, a material (SF2) with n ₀ = 1.647 may be used for the prism.

Since the reflectance of S waves can be increased when the optical path length of each layer is λ / 4, if the film thickness of the high refractive index is d _H and the film thickness of the low refractive index is d _L , then n _H d _H cos θ _H = n _L d _L cos θ _L = λ / 4. The reflectance R _S of the S wave in this case is

[0009]

[Equation 3]

Thus, the reflectance R increases as the number of layers q in the film increases.
_S approaches 1. The reflectance of P-wave is 0 regardless of the film thickness because it satisfies the Brewster angle. Therefore, when non-polarized light is incident on such a polarization beam splitter, P waves are transmitted and S waves are reflected on the film surface.

However, when such a polarization beam splitter is used in a liquid crystal projector, for example, when the incident angle to the film surface is 45 ° and each polarization component needs to be separated, the prism refraction is performed. Since the characteristics are determined by the selection of the refractive index and the refractive index of the multilayer thin film, it is necessary to select a material with a special refractive index to obtain the necessary and sufficient performance as a polarizing beam splitter, or to create a multilayer film with such a material. And becomes expensive. In addition, due to the inherent size of the prism, a large-sized polarization beam splitter cannot obtain uniform in-plane optical characteristics due to the difference in temperature distribution in the uneven thickness portion of the prism. Further, such a prism has a disadvantage that the weight becomes heavy.

In order to solve the above problems, there is, for example, a polarization beam splitter disclosed in Japanese Patent Laid-Open No. 5-181014. In the present invention, the optical block is formed in a stepped shape, but depending on the position of the light ray passing through this block, there are portions where the P wave and the S wave of the polarization component have different distances through the optical block. This means that the optical paths of the light waves of the respective polarization components are different, which may have a significant influence on the characteristics of the polarization beam splitter. In addition, the light incident on the lower surface (the surface parallel to the incident direction) of the stepped optical block at an angle is reflected by the incident surface, and the incident angle on the film surface of the polarization beam splitter may increase. To be

On the other hand, the polarization beam splitter disclosed in Japanese Unexamined Patent Publication No. 5-173020 is designed so that the prisms other than the film surface are made of plastic to reduce the weight and the cost. However, as can be seen from the above equation, in order to obtain the required refractive index performance of the prism, it is necessary to match the refractive index of the material of the film surface part and the refractive index of the plastic part, and in practice, this It is difficult to manage such a refractive index. Further, the problem of uneven thickness still exists, and the problem of non-uniformity of optical properties cannot be solved.

In order to solve this problem, Japanese Patent Laid-Open No. 5-3
There is an invention disclosed in Japanese Patent No. 23121. This is to fill a portion corresponding to a prism with a liquid, and to make the prism uniform by making it a liquid that has been distorted due to the temperature difference. However, there are inconveniences that the joint portion of the housing that is filled with the liquid has to be excellent in waterproofness, and the handling is also required to be careful.

As a device for separating and utilizing a beam by utilizing a cholesteric liquid crystal, for example, Japanese Patent Application Laid-Open No. 4-1 is used.
What is disclosed in Japanese Patent No. 86231 is that a cholesteric liquid crystal separates incident light into right-handed circularly polarized light and left-handed circularly polarized light, and the separated circularly polarized light is made incident on a polymer dispersion type reflective liquid crystal. An image is modulated in a polymer dispersion type reflective liquid crystal. That is, when the polymer-dispersed reflective liquid crystal is for black display, it diffuses the incident circularly polarized light, and for white display, it is reflected as it is to reverse the direction of rotation of circularly polarized light, and is reflected again by the cholesteric liquid crystal. The light is transmitted and guided to a projection lens to project an image. This is an invention characterized by separating a beam into two beams, a clockwise and a counterclockwise, and utilizing it for a reflection type projection. The main purpose is to separate two linearly polarized lights of P wave and S wave which are orthogonal to each other. Not meant to be.

Further, the one disclosed in Japanese Patent Application Laid-Open No. 4-339488 provides an apparatus for reproducing a three-dimensional image as an aerial image, and a cholesteric liquid crystal or a cholesteric liquid crystal is used as means for separating or synthesizing a beam in the configuration. The half-mirror is used so that the separated circularly polarized light is used, and this is not intended to separate into two linearly polarized lights of P wave and S wave which are orthogonal to each other.

Further, in the one disclosed in Japanese Patent Laid-Open No. 7-92445, a cholesteric liquid crystal is arranged in a concave shape in a flat glass, and the selectively reflected light is once condensed and its reflection direction is changed by a mirror. However, this method is not preferable because the intensity distribution or the angle distribution of the light that is selectively reflected from the light that has passed through the cholesteric liquid crystal and then condensed and extracted will change.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and therefore does not use a thick member such as a prism, is light in weight, is excellent in handleability, and has an effect on temperature change. It is an object to be solved to provide a polarization beam splitter which is difficult to receive and a liquid crystal projector using the polarization beam splitter.

[0019]

[0020]

[0021]

According to a first aspect of the present invention, there is provided a polarizing beam splitter having a function of separating emitted light from a light source into P-wave and S-wave polarization components having different vibration planes. As a component of
Two kinds of cholesteric liquid crystal panels having different characteristics from a half mirror and a total reflection mirror and a phase plate provided corresponding to each of the cholesteric liquid crystals are provided, and the half mirror is arranged at a predetermined angle with respect to the emitted light. , The emitted light is separated by the half mirror, the cholesteric liquid crystal and the retardation plate are sequentially arranged on the optical paths of the respective separated lights, and only the clockwise or counterclockwise polarization component is generated by the cholesteric liquid crystal. While being transmitted and made incident on the retardation plate, the polarized component reflected without being transmitted by the cholesteric liquid crystal is re-separated by the half mirror, and the re-separated polarized component is provided on one optical path. The total reflection mirror changes the rotation direction of the re-separated polarization component, returns it to the optical path incident on the total reflection mirror, and makes it enter the retardation plate. The Rukoto, in which to obtain the P-wave and S-wave.

According to a second aspect of the present invention, in the first aspect of the invention, the half mirror is arranged at an angle of 45 ° with respect to the emitted light, and the cholesteric liquid crystal is divided into the respective lights separated by the half mirror. The total reflection mirror is arranged at an angle of 90 ° with respect to one of the polarized components re-separated by the half mirror.

The invention of claim 3 is the even Ru comprise a polarizing beam splitter of the serial <br/> mounting in claim 1 or 2.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a polarization beam splitter according to the present invention will be described in detail with reference to the accompanying drawings.

[0025] below, it will be described with reference to FIG. 1 a block diagram for polarization combining a cholesteric liquid crystal and a retardation plate to obtain a two linearly polarized beams of different 90 °. Figure 1 is a diagram conceptually showing an example of a polarization beam splitter, in the drawing,
1 is a cholesteric liquid crystal, 2a and 2b are glass, 3a,
3b is a λ / 4 retardation plate, 4l and 4r are left-handed circularly polarized light, right-handed circularly polarized light among the light components included in natural light, 5
l is counterclockwise circularly polarized light reflected by cholesteric liquid crystal, 5r
Is a right-handed circularly polarized light transmitted through the cholesteric liquid crystal, 6a,
6b is linearly polarized light.

Although light is explained by the movement of waves, the light emitted from the light source of the projector is so-called natural light, which is a circularly polarized light in which longitudinal waves and transverse waves are not in phase. . Also, in such a circularly polarized state, the clockwise rotation light 4r and the counterclockwise rotation light 4l are mixed.

The cholesteric liquid crystal 1 has a characteristic that light in a certain rotation direction is transmitted and light in the opposite rotation direction is reflected. Therefore, the light transmitted through the cholesteric liquid crystal 1 becomes a circularly polarized light 5r (shown as a right-handed circularly polarized light in the figure) having a certain unidirectional rotation direction, and the reflected light has a rotation direction 5 opposite to that.
It becomes l. On the other hand, the phase plate has a characteristic of changing the phase of light, and in particular, the phase difference plates 3a and 3b having a phase difference of ¼ of the wavelength λ make the incident circularly polarized light linearly polarized light 6a and 6b.
It has the function of converting to b. Therefore, the light transmitted and reflected by the cholesteric liquid crystal 1 is further added to the λ / 4 phase difference plate 3a,
By transmitting 3b, the polarization direction is 90
The light beams 6a and 6b having different linear polarizations are obtained.

In the above example, the cholesteric liquid crystal is 45
Since it is placed at a degree and realizes PS separation, its component parts can be realized by two elements of a cholesteric liquid crystal and a phase plate, resulting in a very simple system. On the other hand, the rotation selective reflection of the cholesteric liquid crystal occurs when light is incident in parallel to the helical axis of the cholesteric liquid crystal, and at this time, circularly polarized light having an optical rotation direction that is the same as the helical axis is reflected. In order to make the incident light parallel to the helical axis in a state of being tilted at 45 °, it is necessary to orient the helical axis of the cholesteric liquid crystal by tilting at 45 °, which increases the difficulty of making the cholesteric liquid crystal.

FIG. 2 is a diagram conceptually showing a configuration of an embodiment of a polarizing beam splitter according to the present invention, Hafumi
More effectively with P-wave using Ra
The S wave is separated. In FIG.
11 is a left-handed transmissive / right-handed reflective cholesteric liquid crystal,
12 is a cholesteric liquid crystal with a clockwise transmission and a counterclockwise reflection,
Reference numerals 13a and 13b denote λ / 4 phase difference plates, 14 denotes a total reflection mirror, 15 denotes a half mirror, and 20 to 42 denote light amounts of light components between respective constituent elements and a rotation direction of light. Here, the incident light of the natural light emitted from the lamp 50 is 100 LR.
The counterclockwise component of this incident light is represented by 100L and the clockwise component is represented by 100R. In the drawings and in the following description, the combination of numbers in the light components and L or R indicates the light amount with respect to the light amount 100 of the incident light, and the rotation direction of the light is expressed as L and R, and It shall indicate the property.

The half mirror 15 is provided with a semi-transmissive film and transmits 50% of light and reflects 50% thereof regardless of polarization. Therefore, the incident light 100LR is incident on the half mirror 15, and the light 21 transmitted through the half mirror 15 and the reflected light 31 are both 50LR.

First, the transmitted light 21 will be described. The transmitted light 21 is incident on the cholesteric liquid crystal 12 having the characteristics of clockwise transmission and counterclockwise reflection. Due to the characteristics of the cholesteric liquid crystal 12, the light 23 transmitted through the cholesteric liquid crystal 12 becomes 50R, and the light 22 reflected on the contrary becomes 50L. The reflected light 22 reaches the half mirror 15 again, and is halved again by the half mirror 15. The reflected light 25 becomes 25R because the rotation direction is changed by the reflection, and the transmitted light 2
4 will be transmitted as 25 L. The transmitted light 24 is lost and dissipated.

On the other hand, 25R reflected by the half mirror 15
The reflected light 26 is reflected again by the total reflection mirror 14, and the reflected light 26 changes its rotation direction due to reflection and becomes 25 L of light and travels to the half mirror 15. Further, in the half mirror 15, the transmitted light 29 becomes 12.5 L and travels toward the cholesteric liquid crystal 11 that is left-handedly transmitted and right-handedly reflected. The other half of the reflected light 27 changes its rotation direction again, 12.5R
Then, it goes to the cholesteric liquid crystal 12 that transmits right-handed and reflects left-handedly. Since this cholesteric liquid crystal 12 has a right-handed transmission characteristic, this 12.5R light 27
Is transmitted through the cholesteric liquid crystal 12 and becomes transmitted light 28. Therefore, 50L that first transmitted through the half mirror 15
R light 21 to 50R light 23 and 12.5R light 2
The light of 62.5R which is the total of 8 is transmitted through the cholesteric liquid crystal 12 that is transmitted in the clockwise direction and is reflected in the counterclockwise direction, and the light of 12.5L is transmitted through the other cholesteric liquid crystal 11.

Next, let us first consider 50 LR light 31 reflected by the half mirror 15. Cholesteric liquid crystal 11
In contrast to the above-mentioned cholesteric liquid crystal 12, has a left-handed transmission / right-handed reflection characteristic. The reflected light 31 also exhibits the same behavior as described above. First, of the 50 LR light 31 that has entered the cholesteric liquid crystal 11, 50 L is transmitted as transmitted light 32 and 50 R is reflected as reflected light 33, and this reflected light 33 is directed to the half mirror 15. In the half mirror 15, the reflected light 35 is 2
It becomes 5 L and is dissipated as loss light, and the transmitted light 34 becomes 25 R and is transmitted. Then, the transmitted light 34 is reflected by the total reflection mirror 14 to become 25 L of reflected light 36. This 2
Of the 5L light 36, the reflected light 37 becomes 12.5R and goes to the cholesteric liquid crystal 12 that transmits right and left, and the transmitted light 39 becomes 12.5L and the cholesteric that transmits and rotates counterclockwise. It goes to the liquid crystal 11. Therefore, 62.5 L of light, which is the total of 50 L of light 32 and 12.5 L of light 40 with respect to the reflected light 31 at the first half mirror 15, is transmitted through the cholesteric liquid crystal 11 that is counterclockwise transmitted / clockwise reflected. The 12.5R light 28 is transmitted and is transmitted through the other cholesteric liquid crystal 12.

From the above results, the light components finally transmitted through the cholesteric liquid crystals 12 and 11 are generated in the cholesteric liquid crystals 12 and 11, respectively.
The light 41 is 75R and the light 42 is 75L. When the polarization directions are separated only by the half mirror and the polarizing plate, the obtained light components are 50R and 50L, but by arranging the cholesteric liquid crystal and the total reflection mirror in this way, It is possible to effectively use the light and to separate the polarization directions.

In this embodiment, the number of half mirrors, total reflection mirrors, two kinds of cholesteric liquid crystals, the phase plate and its constituent elements are increased, but the incident angle to the cholesteric liquid crystal is 0.
Since the incident light is incident at an angle of ° and the helical axis of the cholesteric liquid crystal is created in parallel alignment, the creation is easy. Further, as described above, half of the light reflected by the cholesteric liquid crystal can be used, as compared with the case where the light separated by the half mirror is converted into linearly polarized light by the polarizing plate, which is a more effective means.

[0036] Next Ide, illustrating a liquid crystal projector using the polarizing beam splitter according to the present invention with reference to FIG. FIG. 3 is a diagram conceptually showing the configuration of an embodiment of a liquid crystal projector including a polarization beam splitter according to the present invention. In the figure, 50 is a light source (lamp) having a parabolic reflector, and 51 is a polarization separation first unit. 1 is a cholesteric liquid crystal, 52 is a second cholesteric liquid crystal for polarization combination,
53a, 53b, 53c, 53d are λ / 4 phase difference plates, 5
4a and 54b are total reflection mirrors, 55a and 55b are incident polarization plates, 56a and 56b are emission polarization plates, 57a and 57b are image forming liquid crystal panels, 58 is a projection lens, 59 is a screen, and natural light is emitted from the light source 50. Shall be emitted.

In this embodiment, two cholesteric liquid crystals 51, 52 arranged at 45 ° having the structure shown in FIG. 1 are used .
And a polarization beam splitter composed of phase difference plates 53a to 53d, two image forming liquid crystal panels 57a, 57 are used.
b is arranged to configure a liquid crystal projector. In the lamp 50, the light emitted from the light source is condensed by the reflector and is incident on the first cholesteric liquid crystal 51. The first cholesteric liquid crystal 51 transmits only light in one rotation direction and reflects light in reverse rotation. The light transmitted or reflected by the first cholesteric liquid crystal 51 is converted into linearly polarized light having different phases by the λ / 4 retardation plates 53a and 53b. The light converted into the linearly polarized light is reflected by the total reflection mirrors 54a and 54b,
The light enters the incident polarization plates 55a and 55b. The light here is
Although the linearly polarized light has already been formed by the λ / 4 phase difference plates 53a and 53b, the degree of linear polarization is further increased by the incident polarization plates 55a and 55b. This is to increase the contrast as a liquid crystal projector. The light transmitted through the incident polarization plates 55a and 55b is used as the image forming liquid crystal panels 57a and 57b and the emission polarization plate 5, respectively.
6a and 56b are transmitted. Liquid crystal panel 57a,
57b, the output polarizing plates 56a, 5 are modulated.
The linearly polarized light emitted from 6b is reflected by the λ / 4 phase difference plates 53d, 5d.
By passing through 3c, circularly polarized light in the original rotation direction is obtained again. Second cholesteric liquid crystal 52 for polarization combination
Has the same characteristics as the first cholesteric liquid crystal 51 on the incident side, the light is recombined, and the projection lens 58
The combined image is projected on the screen 59 via.

[0038]

Effects of the Invention By constituting the polarization beam splitter the invention of this, a thick member such as a prism is not required, setting of the prism material and the refractive index of the multilayer thin film in those using prisms, by vapor deposition or the like The step of forming the multi-layered thin film can be omitted, the non-uniform optical characteristics generated in the plane due to the temperature difference of the prism can be eliminated, and a lightweight and inexpensive polarization beam splitter can be obtained.

[0039]

[0040] In addition, the angle of incidence on the cholesteric liquid crystal 0
Since the incident light is incident at an angle of ° and the helical axis of the cholesteric liquid crystal is created in parallel alignment, the creation is easy. Further, as compared with the case where the light separated by the half mirror is converted into the linearly polarized light by the polarizing plate, half of the light reflected by the cholesteric liquid crystal can be used, which is a more effective means.

By constructing a liquid crystal projector using the polarization beam splitter of the present invention, it is possible to obtain a liquid crystal projector which is lightweight and inexpensive and which is not easily affected by the temperature on the image quality.

[Brief description of drawings]

1 is a diagram conceptually showing an example of a polarization beam splitter.

FIG. 2 is a diagram conceptually showing the configuration of one embodiment of a polarization beam splitter according to the present invention.

FIG. 3 is a diagram conceptually showing the structure of an embodiment of a liquid crystal projector including a polarization beam splitter according to the present invention.

[Explanation of symbols]

1 ... Cholesteric liquid crystal, 2a, 2b ... Glass, 3a,
3b ... λ / 4 phase difference plate, 4l, 4r ... Left-handed circularly polarized light, right-handed circularly polarized light of natural light, 5l ... Reflected left-handed circularly polarized light, 5r ... Transmitted right-handed circularly polarized light, 6a, 6b ...
Linearly polarized light, 11 ... Counterclockwise transmission / clockwise reflection type cholesteric liquid crystal, 12 ... Clockwise transmission / counterclockwise reflection type cholesteric liquid crystal, 13a, 13b ... λ / 4 phase difference plate, 14 ... Total reflection mirror, 15 ... Half mirror 20 to 42 ... Representing the amount of light and the optical rotation direction of the light component between the respective components, 50 ...
Light source (lamp) equipped with parabolic reflector, 51 ...
First cholesteric liquid crystal for polarization separation, 52 ... Second cholesteric liquid crystal for polarization combination, 53a, 53b, 5
3c, 53d ... λ / 4 retardation plate, 54a, 54b ... Total reflection mirror, 55a, 55b ... Incident polarization plate, 56a, 56
b ... Emitting polarization plate, 57a, 57b ... Image forming liquid crystal panel, 58 ... Projection lens, 59 ... Screen.

Claims (3)

(57) [Claims] 1. A polarization beam splitter having a function of separating light emitted from a light source into P-wave and S-wave polarization components having different vibration planes, wherein a half mirror and a total reflection mirror are provided as constituent elements of the polarization beam splitter. And two kinds of cholesteric liquid crystals having different characteristics and a phase plate provided corresponding to each of the cholesteric liquid crystals, and the half mirror is arranged at a predetermined angle with respect to the emitted light,
The emitted light is separated by the half mirror, the cholesteric liquid crystal and the retardation plate are sequentially arranged on the optical paths of the respective separated lights, and only the clockwise or counterclockwise polarized component is transmitted by the cholesteric liquid crystal. While allowing the light to enter the retardation plate, the polarization component that is reflected by the cholesteric liquid crystal without being transmitted is re-separated by the half mirror, and all the components provided on one optical path of the re-separated polarization component are separated. By changing the rotation direction of the re-separated polarization component by the reflection mirror and returning it to the optical path incident on the total reflection mirror and making it enter the retardation plate,
Polarization beam splitter characterized in that it obtains a wave and an S wave. 2. The half mirror is arranged at an angle of 45 ° with respect to the emitted light, and the cholesteric liquid crystal is 90 ° with respect to each light separated by the half mirror.
Angle in place, the polarization beam splitter according to claim 1, wherein the total reflection mirror is characterized in that to arrange While an angle of 90 ° to the polarization component that is re-separated by the half mirror. 3. A liquid crystal projector comprising the polarization beam splitter according to claim 1 .